docs: def current_line(self):
          '''Get the text of the current source line as a string, with a trailing
          newline character'''
          if self.is_optimized_out():
              return '(frame information optimized out)'
          with open(self.filename(), 'r') as f:
              all_lines = f.readlines()
              # Convert from 1-based current_line_num to 0-based list offset:
              return all_lines[self.current_line_num()-1]